refactor: rename think_deeper to thinkdeep for brevity

- Renamed `think_deeper` tool to `thinkdeep` for shorter, cleaner naming
- Updated all imports from ThinkDeeperTool to ThinkDeepTool
- Updated all references from THINK_DEEPER_PROMPT to THINKDEEP_PROMPT
- Updated tool registration in server.py
- Updated all test files to use new naming convention
- Updated README documentation to reflect new tool names
- All functionality remains the same, only naming has changed

This completes the tool renaming refactor for improved clarity and consistency.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/test_server.py

@@ -19,7 +19,7 @@ class TestServerTools:
         tool_names = [tool.name for tool in tools]
 
         # Check all core tools are present
-        assert "think_deeper" in tool_names
+        assert "thinkdeep" in tool_names
         assert "codereview" in tool_names
         assert "debug" in tool_names
         assert "analyze" in tool_names
@@ -77,4 +77,4 @@ class TestServerTools:
         response = result[0].text
         assert "Gemini MCP Server v" in response  # Version agnostic check
         assert "Available Tools:" in response
-        assert "think_deeper" in response
+        assert "thinkdeep" in response